Crush-resistant disposable lid

ABSTRACT

A crush-resistant, preferably thermoformed, disposable lid is provided for plates, platters, bowls and the like. The lid includes a dome and a downwardly extending sidewall provided with a plurality of outwardly convex flutes formed in the sidewall with a characteristic cylindrical diameter. The sidewall extends from the dome to an engagement portion adapted to be secured to the plate, platter or bowl about an engagement perimeter of the lid. There are typically fewer than about 1.85 flutes per inch of engagement perimeter and the flutes are characterized by a ratio of the characteristic cylindrical diameter of the flutes to the engagement perimeter of the lid of at least about 0.0125.

CLAIM FOR PRIORITY

[0001] This non-provisional application claims the benefit of the filing date of U.S. Provisional Patent Application Serial No. 60/305,225, filed Jul. 13, 2001, of the same title.

TECHNICAL FIELD

[0002] The present invention relates generally to disposable lids, such as those used with paper plates, platters, bowls and the like and more particularly to a crush-resistant lid provided with relatively large, outwardly convex flutes in specified frequency about the perimeter.

BACKGROUND

[0003] Disposable lids of the general class of the invention are generally employed in connection with disposable plates, platters, bowls and the like items; perhaps most typically such plates, platters and bowls are made of paper, plastic or foil. Since it is highly desirable to make disposable lids as lightweight as possible, lid rigidity and especially crush-resistance are frequently product issues. Finite element analysis was used to identify design features that impart crush-resistance to thermoformed lids and new lids with superior crush-resistance were produced in accordance with the present invention.

SUMMARY OF INVENTION

[0004] There is provided in accordance with the present invention a crush-resistant disposable lid made from a thermoplastic material for plates, platters, bowls and the like including a dome portion with generally planar upper surface portion and a downwardly extending sidewall about its periphery provided with a plurality of outwardly convex flutes formed in the sidewall. The flutes have a characteristic cylindrical diameter and the sidewall extends downwardly to an engagement portion of the lid adapted to be secured to the plate, platter or bowl about an engagement perimeter of the lid, wherein the lid includes about 1.85 or fewer flutes per inch of engagement perimeter.

[0005] A preferred embodiment of the invention is a thermoformed, crush-resistant disposable lid for plates, platters, bowls and the like including a dome portion with a generally planar upper surface portion and a downwardly extending sidewall provided with a plurality of outwardly convex flutes formed in the sidewall wherein the flutes are provided with a characteristic cylindrical diameter. The sidewall extends downwardly to an engagement portion of the lid adapted to be secured to the plate, platter or bowl about an engagement perimeter of the lid which includes about 1.85 or fewer flutes per inch of engagement perimeter. The lid is further characterized by a ratio of the characteristic cylindrical diameter of the flutes to the engagement perimeter of the lid of at least about 0.0125.

BRIEF DESCRIPTION OF DRAWINGS

[0006] The invention is described in detail below with reference to the appended figures wherein like numerals indicate like parts and wherein:

[0007]FIG. 1 is a view in perspective of a disposable lid configured in accordance with the invention having 50 flutes;

[0008]FIG. 2 is a sectional plan view of the periphery of the sidewall of the lid of FIG. 1 along line 2-2;

[0009]FIG. 3 is a sectional schematic view in elevation of the lid profile from center along the centerline of a flute of the lid of FIG. 1 at line 3-3;

[0010]FIG. 4 is a sectional schematic view in elevation of the lid profile from center along an unfluted portion of the lid of FIG. 1 at line 4-4;

[0011]FIG. 5 is a schematic view comparing the profiles of a fluted portion (FIG. 3) and unfluted portion (FIG. 4) of the disposable lid of FIG. 1;

[0012]FIG. 6 is a sectional schematic view in elevation along line 6-6 of FIG. 1, showing the profile of the removal tab;

[0013]FIG. 7 is a schematic view illustrating the profile of a stepped lid;

[0014]FIG. 8 is a partial perspective view illustrating crush-testing of a disposable lid;

[0015]FIG. 9 is a plot of applied load versus simulated deflection for various lid designs having different numbers of flutes;

[0016]FIG. 10 is a plot of load versus simulated deflection for lids with various flute diameters;

[0017]FIG. 11 is a plot of load versus simulated deflection for lids with flutes having various inward extensions about the dome;

[0018]FIG. 12 is a plot of load versus simulated deflection for lids having 50 flutes and various flute heights;

[0019]FIG. 13 is a plot of load versus simulated deflection for various fluted and unfluted lid designs;

[0020]FIG. 14 is a plot of load versus simulated deflection for various lids of unstepped and stepped sidewall profile; and

[0021]FIG. 15 is a plot comparing load versus simulated deflection characteristics of the lid of FIG. 1 with another lid.

DETAILED DESCRIPTION

[0022] The invention is described in detail below with reference to particular embodiments for purposes of illustration and exemplification only; modifications to these embodiments within the spirit and scope of the invention will be readily apparent to one of skill in the art.

[0023] Referring to FIGS. 1 through 6, there is illustrated a crush-resistant disposable lid 10 made from a thermoplastic material for plates, platters, bowls and the like including a dome portion 11 with a generally planar upper surface portion 12 and a downwardly extending sidewall 14 provided with a plurality of outwardly convex flutes such as flutes 16-30 formed in the sidewall with a characteristic cylindrical diameter. The sidewall extends downwardly to an engagement portion 32 of the lid adapted to be secured to a plate, platter or bowl about an engagement perimeter 34 of the lid. Typically, the lid includes about 1.85 or fewer flutes per inch of engagement perimeter; suitably from about 1.5 to about 1.85 flutes per inch of engagement perimeter, with from about 1.6 to about 1.75 flutes per inch of engagement perimeter being preferred in some embodiments. The lid illustrated in FIG. 1 has about 1.7 flutes per inch of engagement perimeter; that is 50 flutes about 30 inches for a 9½″ diameter plate, for example.

[0024] The inventive lid could alternatively be in an oval shape for an oval platter having axes of about 9″ and 6½ inches wherein it has an engagement perimeter of about 25½ inches and 44 flutes in its sidewall.

[0025] Inventive lid 10 has unfluted sidewall portions such as portions 36-40 between flutes. It is not necessary to add fillets transitioning between the fluted and unfluted portions of the sidewall with the inventive design as will be appreciated from the deflection data which follows. There is further provided a stepped removal tab 42 which is used to disengage the lid from a plate.

[0026] The geometry of the sidewall is better appreciated by reference to FIG. 2 which is a plan view in section along line 2-2 of FIG. 1. Flute 20 is shaped as a partial surface of an inclined outwardly convex cylinder (convex about its outer surface), which may be inclined 10°, 15° or so with respect to a perpendicular upper surface portion 12 of dome 11 or the upper surface of engagement portion 32; that is, a 10° or 15° sidewall angle. The cylinder has a characteristic radius which is the radius of curvature, r, of flute 20. Thus, the flute may be said to have a characteristic cylindrical diameter, D, of twice the radius of curvature of the flute. In the embodiment shown, the flutes have the same characteristic cylindrical diameter; however, there may be flutes of other configuration interspersed without departing from the spirit and scope of the invention.

[0027] The various features of the profile of the lid are perhaps best illustrated in FIGS. 3, 4 and 5. The sidewall extends downwardly to engagement portion 32 about the perimeter of the lid which includes an undercut groove 44 provided with an undercut portion 46. Undercut groove 44 extends about substantially the entire periphery of lid 10 (except at tab 42) so as to form a continuous seal when engaged to a plate, platter, bowl or the like by way of its undercut portion 46. Groove 44 thus defines at its outer wall the engagement perimeter 34 which has a length of about 30 inches or so when configured for a 9½″ diameter plate as in FIG. 1.

[0028]FIG. 3 is a view in section and elevation along line 3-3 in FIG. 1 showing the profile of lid 10 from center along the center of flute 24; whereas, FIG. 4 is a view in section and elevation showing unfluted portion 36 of sidewall 14. FIG. 5 is a schematic diagram illustrating the relative dimensions of the profiles of FIGS. 3 and 4. Along the central area of the dome portion 11, the profiles are substantially identical, whereas at outer portion 48, the fluted portion 24 is shown in a dashed line and unfluted portion 36 is shown in a solid line. The unfluted areas are slightly raised at 48, whereas the flutes have a substantial height. At the engagement periphery, the profiles are again identical. Fluted portion 24 projects upwardly a distance 50 at the top portion with respect to unfluted portion 36 and outwardly a distance 52 with respect to the unfluted sidewall as shown in FIG. 5. This distance is referred to herein as the flute height. So also, fluted portion 24 an inward extension length 52, as shown, which is generally the inward distance from corner 54 that a flute 24 is raised above the unfluted portion of dome 11.

[0029] The flutes may have a characteristic cylindrical diameter of from about 0.4 inches to about 0.6 inches in the embodiment of FIG. 1, preferably about 0.5 inches. The ratio of the characteristic cylindrical diameter of the flutes to the engagement perimeter of said lid is typically at least about 0.0125, and preferably the ratio of the characteristic cylindrical diameter of the flutes to the engagement perimeter of said lid is from about 0.0125 to about 0.025. In the embodiment of FIG. 1, the ratio of the characteristic cylindrical diameter of the flutes to the engagement perimeter of the lid is about 0.018.

[0030] The inward extension length of the flutes may be at least about 0.35 inches and is sometimes at least about 0.5 inches. The ratio of the inward extension length of the flutes to the engagement perimeter may be from about 0.015 to about 0.04. In the embodiment of FIG. 1, the ratio of the inward extension length of the flutes to the engagement perimeter is about 0.02.

[0031] The lid is typically thermoformed, thermoformed by the application of vacuum or thermoformed by a combination of vacuum and pressure from a sheet of thermoplastic material. Generally speaking, thermoforming is the pressing and/or stretching of heated deformable material into final shape. In the simplest form, thermoforming is the draping of a softened sheet over a shaped mold. In the more advanced form, thermoforming is the automatic high speed positioning of a heated sheet having an accurately controlled temperature into a pneumatically actuated forming station whereby the article's shape is defined by the mold, followed by trimming and regrind collection as is well known in the art. Forming techniques other than conventional thermoforming are also suitable for the manufacture of articles described in the present invention. These include variations such as presoftening the extruded sheet to temperatures below the final melting temperature, cutting flat regions (i.e., blanks) from the sheet, transfer of blanks by gravity or mechanical means into matched molds whereby the blanks are shaped into the article by heat and pressure. The sheet from which the blanks have been cut out is collected as regrind and is recyclable. Conventional paperboard pressing equipment and corresponding forming tooling is optionally modified to produce articles of this invention. Still other alternative arrangements include the use of drape, vacuum, pressure, free blowing, matched die, billow drape, vacuum snap-back, billow vacuum, plug assist vacuum, reverse draw with plug assist, pressure bubble immersion, trapped sheet, slip, diaphragm, twin-sheet cut sheet, twin-sheet rolled forming any suitable combinations of the above. Details are provided in J. L. Throne's book, Thermoforming, published in 1987 by Coulthard. Pages 21 through 29 of that book are incorporated herein by reference. Suitable alternate arrangements also include a pillow forming technique which creates a positive air pressure between two heat softened sheets to inflate them against a clamped male/female mold system to produce a hollow product. Metal molds are etched with patterns ranging from fine to coarse in order to simulate a natural or grain like texturized look. Suitable formed articles are trimmed in line with a cutting die and regrind is optionally reused since the material is thermoplastic in nature. Other arrangements for productivity enhancements include the simultaneous forming of multiple articles with multiple dies in order to maximize throughput and minimize scrap.

[0032] Generally, the lid has a wall caliper of from about 8 to about 20 mils, preferably from about 8 to about 15 mils, and more preferably from about 10 to about 13 mils. In some embodiments, the lid is thermoformed by the application of vacuum. Typical materials include oriented polystyrene sheet and thermoplastic materials comprising polypropylene.

[0033] In preferred embodiments, the engagement portion of the lid includes an undercut groove such as groove 44 extending substantially continuously about the engagement perimeter.

[0034] In typical lids of the invention, the flutes have a flute height of greater than about 0.075 inches, preferably from about 0.075 to about 0.125 inches.

[0035] Lid 10 includes a removal tab 42 which is illustrated in more detail in FIG. 6. FIG. 6 is a view in section along line 6-6 of FIG. 1 showing the profile from center along the middle portion of tab 42. Dome 11 extends outwardly to flute 30 which extends downwardly to an upper step 56. Step 56 extends outwardly from center to a downward projecting sidewall portion 58 which, in turn, transitions to a lower step 60. The outer portion 62 of the tab extends further downwardly as shown in FIG. 6. Tab 42 thus defines an upwardly extending cavity 64 where a user can insert a finger or thumb to remove lid 10 from a plate, platter or bowl. The relative position of the cavity is illustrated with respect to undercut groove 44 and including undercut 46 in the diagram in phantom lines. It can be seen that cavity 64 extends upwardly with respect to engagement perimeter 34. In the embodiment of FIG. 1 and following, sidewall 14 extends downwardly in a substantially linear, continuous manner from upper surface portion 12 to engagement perimeter 34 as is illustrated in FIGS. 3 through 6 in particular. It is likewise possible to have a “stepped” profile as is shown schematically in FIG. 7.

[0036] In FIG. 7 there is shown a profile of a lid 66 having a generally planar dome portion 68 and a fluted sidewall 70. Fluted sidewall 70 extends downwardly to a step 72 which extends outwardly to a corner 74. Unfluted sidewall 75 extends downwardly to an engagement portion 76 including an undercut groove 78 which, in turn, transitions to an outermost portion 80. The step height is the distance between corner 74 and engagement portion 76.

[0037] Finite element analysis (FEA) modeling was used to quantify the impact of various features on the crush-resistance of disposable lids. The analysis included FEA modeling of an Instron crush test in which the force required to depress the center of the lid with a 4″ diameter probe is measured, as is illustrated in FIG. 8. Various results for simulated crush-resistance are plotted in FIGS. 9 through 15 for a lid of the class illustrated above. FIG. 9 is a plot of applied load versus deflection for various lid designs having different numbers of flutes wherein it can be seen that fewer flutes are preferred. FIG. 10 is a plot of load versus deflection for lids with various flute diameters, wherein it can be seen that larger flute diameters are preferred.

[0038]FIG. 11 is a plot of load versus deflection for lids with flutes having various inward extension lengths about the dome. Generally, a larger inward extension gave better characteristics.

[0039]FIG. 12 is a plot of load versus deflection for lids having 50 flutes and various flute heights. Here, higher flutes gave generally better crush-resistance.

[0040]FIG. 13 is a plot of load versus deflection for various fluted and unfluted lid designs. Total elimination of flutes improves crush-resistance in the center, but degrades crush-resistance at the lid's outer edge. FIG. 14 is a plot of load versus deflection for various lids of unstepped and stepped sidewall profile. A step in the sidewall reduces crush-resistance which decreases with increasing step height.

[0041]FIG. 15 is a plot comparing load versus deflection characteristics of the lid of FIG. 1 with another lid.

[0042] In order to evaluate consumer perception of strength and sturdiness of lids, individuals were randomly selected to evaluate prototype lids and current commercial products. The lids were placed on a substrate plate and the panelists were asked to rank the lids for sturdiness on scales of 1-10, 1-4 and 1-7 with 1 being the sturdiest. Prototype C lids were generally of the geometry of the lid of FIGS. 1-6, except that prototype C lids had slightly more than 2 flutes per inch of engagement. Prototype C12.5 had a 12.5 mil wall caliper, whereas prototype C10 had a roughly 10 mil thickness. Prototype A and B lids were generally of the geometry of the lid of FIGS. 1-6 above having an approximately 30 inch engagement perimeter and 50 flutes. Prototype A lids had a 10° sidewall angle, while prototype B lids had a 15° sidewall angle. Prototypes A12.5 and A10 had a 12.5 mil and 10 mil wall caliper respectively as did prototypes B12.5 and B10. Results of comparisons appear in Tables 1, 2 and 3 for lids of various caliper in thousandths of an inch (mils). TABLE 1 Ranking of Prototype C12.5 Lid vs. Conventional Lids Lid Caliper, mil Ranking Conventional Lid 1, 10 inch 13.1 2.8 Prototype C12.5 12.5 3.1 Conventional Lid 2, 10 inch 12.7 7.5 Conventional Lid 3, 10 inch 10.4 8.7 Conventional Lid 4, 9 inch 12.7 10.0 Conventional Lid 5, 10 inch 10.3 10.4

[0043] TABLE 2 Ranking of Lid Alternatives Lid Caliper, mil Ranking Prototype C12.5 12.5 1.1 Prototype A10 10.0 2.6 Prototype B10 10.0 2.6 Prototype C12.5 10.0 3.7

[0044] TABLE 3 Prototype A Lids vs. Conventional Lids Lid Caliper, mil Ranking Prototype A12.5 12.5 1.5 Conventional Lid 1, 10 inch 13.1 2.4 Prototype A10 10.0 2.5 Conventional Lid 2, 10 inch 12.7 4.2 Conventional Lid 3, 10 inch 10.4 5.3 Conventional Lid 4, 9 inch 12.7 6.6

[0045] As will be appreciated from the data, the lids of the invention were ranked sturdier than other lids of like caliper.

[0046] So also, lids were compared in actual crush tests such as those described above in connection with FIG. 8. Results for Prototype A and C designs for 10 mil and 12.5 mil wall calipers appear in Table 4 below. TABLE 4 Cali- Deflection, inches per, 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Lid mils Force for Deflection, grams Prototype 10 0 573 706 1007 1326 1713 2004 2187 A10 mil Prototype 12.5 0 919 1037 1348 1939 2401 2928 3414 A12.5 mil Prototype 10 0 545 675 874 1096 1258 1418 1547 C10 mil Prototype 12.5 0 819 980 1321 1785 2175 2476 2733 C12.5 mil

[0047] As will be appreciated from Table 4, the Prototype A designs exhibited superior crush-resistance.

[0048] While the invention has been described in connection with numerous features, modifications within the spirit and scope of the present invention, set forth in the appended claims, will be readily apparent to one of skill in the art. 

What is claimed is:
 1. A crush-resistant disposable lid made from a thermoplastic material for plates, platters, bowls and the like comprising a dome having a generally planar upper surface portion and a downwardly extending sidewall provided with a plurality of outwardly convex flutes formed in said sidewall, said flutes having a characteristic cylindrical diameter, said sidewall extending downwardly to an engagement portion of said lid adapted to be secured to said plate, platter or bowl about an engagement perimeter of said lid, wherein said lid includes about 1.85 or fewer flutes per inch of engagement perimeter.
 2. The crush-resistant disposable lid according to claim 1, wherein said lid includes from about 1.5 to about 1.85 flutes per inch of engagement perimeter.
 3. The crush-resistant disposable lid according to claim 2, wherein said lid includes from about 1.6 to about 1.75 flutes per inch of engagement perimeter.
 4. The crush-resistant disposable lid according to claim 2, wherein said lid includes about 1.7 flutes per inch of engagement perimeter.
 5. The crush-resistant disposable lid according to claim 1, wherein said flutes have a characteristic cylindrical diameter of from about 0.4 inches to about 0.6 inches.
 6. The crush-resistant disposable lid according to claim 5, wherein said flutes have a characteristic cylindrical diameter of about 0.5 inches.
 7. The crush-resistant disposable lid according to claim 1, wherein the ratio of the characteristic cylindrical diameter of said flutes to the engagement perimeter of said lid is at least about 0.0125.
 8. The crush-resistant disposable lid according to claim 7, wherein the ratio of the characteristic cylindrical diameter of said flutes to the engagement perimeter of said lid is from about 0.0125 to about 0.025.
 9. The crush-resistant disposable lid according to claim 8, wherein the ratio of the characteristic cylindrical diameter of said flutes to the engagement perimeter of said lid is about 0.018.
 10. The crush-resistant disposable lid according to claim 1, wherein the inward extension length of said flutes is at least about 0.35 inches.
 11. The crush-resistant disposable lid according to claim 10, wherein the inward extension length of said flutes is at least about 0.5 inches.
 12. The crush-resistant disposable lid according to claim 1, wherein the ratio of the inward extension length of said flutes to the engagement perimeter is from about 0.015 to about 0.04.
 13. The crush-resistant disposable lid according to claim 12, wherein the ratio of the inward extension length of said flutes to the engagement perimeter is about 0.02.
 14. The crush-resistant disposable lid according to claim 1, wherein said lid is thermoformed, thermoformed by the application of vacuum or thermoformed by a combination of vacuum and pressure from a sheet of thermoplastic material.
 15. The crush-resistant disposable lid according to claim 14, wherein said lid has a wall caliper of from about 8 to about 20 mils.
 16. The crush-resistant disposable lid according to claim 15, wherein said lid has a wall caliper of from about 8 to about 15 mils.
 17. The crush-resistant disposable lid according to claim 16, wherein said lid has a wall caliper of from about 10 to about 13 mils.
 18. The crush-resistant disposable lid according to claim 14, thermoformed by the application of vacuum.
 19. The crush-resistant disposable lid according to claim 14, thermoformed from oriented polystyrene sheet.
 20. The crush-resistant disposable lid according to claim 14, thermoformed from a sheet of thermoplastic material comprising polypropylene.
 21. The crush-resistant disposable lid according to claim 1, wherein said engagement portion of said lid includes an undercut groove extending substantially continuously about said engagement perimeter.
 22. The crush-resistant disposable lid according to claim 1, wherein said engagement portion of said lid includes a removal tab defining an upwardly extending cavity.
 23. The crush-resistant disposable lid according to claim 22, wherein said removal tab is a stepped removal tab.
 24. The crush-resistant disposable lid according to claim 22, wherein said engagement portion of said lid includes an undercut groove and said upwardly extending cavity of said removal tab extends upwardly with respect to the undercut portion of said groove.
 25. The crush-resistant disposable lid according to claim 1, wherein said sidewall extends downwardly from said dome portion to said engagement portion in a substantially linear manner.
 26. The crush-resistant disposable lid according to claim 1, wherein said flutes have a flute height of greater than about 0.075 inches.
 27. The crush-resistant disposable lid according to claim 26, wherein said flutes have a flute height of from about 0.075 to about 0.125 inches.
 28. A thermoformed, crush-resistant disposable lid for plates, platters, bowls and the like comprising a dome having a generally planar upper surface portion and a downwardly extending sidewall provided with a plurality of outwardly convex flutes formed in said sidewall, said flutes having a characteristic cylindrical diameter and said sidewall extending downwardly to an engagement portion adapted to be secured to said plate, platter or bowl about an engagement perimeter of said lid, wherein said lid includes about 1.85 or fewer flutes per inch of engagement perimeter, said flutes being characterized by a ratio of the characteristic cylindrical diameter of said flutes to the engagement perimeter of said lid of at least about 0.0125.
 29. A thermoformed, crush-resistant disposable lid according to claim 28, wherein said flutes have a characteristic cylindrical diameter of from about 0.4 inches to about 0.6 inches.
 30. A thermoformed, crush-resistant disposable lid according to claim 29, wherein said flutes have a characteristic cylindrical diameter of about 0.5 inches.
 31. The crush-resistant disposable lid according to claim 28, wherein said lid includes from about 1.5 to about 1.85 flutes per inch of engagement perimeter.
 32. The crush-resistant disposable lid according to claim 28, wherein said lid includes from about 1.6 to about 1.75 flutes per inch of engagement perimeter.
 33. The crush-resistant disposable lid according to claim 32, wherein said lid includes about 1.7 flutes per inch of engagement perimeter.
 34. The crush-resistant disposable lid according to claim 28, wherein the ratio of the characteristic cylindrical diameter of said flutes to the engagement perimeter of said lid is from about 0.0125 to about 0.025.
 35. The crush-resistant disposable lid according to claim 31, wherein the ratio of the characteristic cylindrical diameter of said flutes to the engagement perimeter of said lid is about 0.018.
 36. The crush-resistant disposable lid according to claim 28, wherein the inward extension length of said flutes is at least about 0.35 inches.
 37. The crush-resistant disposable lid according to claim 36, wherein the inward extension length of said flute is at least about 0.5 inches.
 38. The crush-resistant disposable lid according to claim 28, wherein the ratio of the inward extension length of said flutes to the engagement perimeter is from about 0.015 to about 0.025.
 39. The crush-resistant disposable lid according to claim 38, wherein the ratio of the inward extension length of said flutes to the engagement perimeter is about 0.02.
 40. The crush-resistant disposable lid according to claim 28, wherein said lid is thermoformed by the application of vacuum or thermoformed by a combination of vacuum and pressure from a sheet of thermoplastic material.
 41. The crush-resistant disposable lid according to claim 40, wherein said lid has a wall caliper of from about 8 to about 20 mils.
 42. The crush-resistant disposable lid according to claim 41, wherein said lid has a wall caliper of from about 8 to about 15 mils.
 43. The crush-resistant disposable lid according to claim 42, wherein said lid has a wall caliper of from about 10 to about 13 mils.
 44. The crush-resistant disposable lid according to claim 40, thermoformed by the application of vacuum.
 45. The crush-resistant disposable lid according to claim 40, thermoformed from oriented polystyrene sheet.
 46. The crush-resistant disposable lid according to claim 40, thermoformed from a sheet of thermoplastic material comprising polypropylene.
 47. The crush-resistant disposable lid according to claim 28, wherein said engagement portion of said lid includes an undercut groove extending substantially continuously about said engagement perimeter.
 48. The crush-resistant disposable lid according to claim 28, wherein said engagement portion of said lid includes a removal tab defining an upwardly extending cavity.
 49. The crush-resistant disposable lid according to claim 48, wherein said removal tab is a stepped removal tab.
 50. The crush-resistant disposable lid according to claim 48, wherein said engagement portion of said lid includes an undercut groove and said upwardly extending cavity of said removal tab extends upwardly with respect to the undercut portion of said groove.
 51. The crush-resistant disposable lid according to claim 28, wherein said sidewall extends downwardly from said dome portion to said engagement portion in a substantially linear manner.
 52. The crush-resistant disposable lid according to claim 28, wherein said flutes have a flute height of greater than about 0.075 inches.
 53. The crush-resistant disposable lid according to claim 52, wherein said flutes have a flute height of from about 0.075 to about 0.125 inches. 